I. Field of the Invention
The present invention relates generally to spectacle lens blanks and, more particularly, to an aspheric spectacle lens blank.
II. Description of the Prior Art
The previously known spectacle lens blanks typically comprise a spherical front convex surface and a spherical concave rear surface. The front and rear surfaces of the lens are formed on different radii of curvature thus providing the desired light refraction for the lens. This refraction varies between a positive amount (to correct farsightedness) and a minus amount (to correct nearsightedness).
Although these previously known lenses have adequately corrected vision for the users, they necessarily result in a relatively thick lens around the outer periphery for high negative refraction lenses and a relatively thick central portion of the lens for relatively high positive refraction lenses. These previously known lenses are not only relatively heavy and therefore uncomfortable to wear, but are also unsightly. Such thick lenses also exhibit chromatic aberration around the outer periphery of the lens for high power lenses, and spherical aberration.